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Mixed-Valent Dinuclear Nickel Complexes Enabled by an Expanded PNNP Pincer Ligand
Anthony J Chavez1, William Buratto1, Phan N Phu2
1Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States.
Inorganic Chemistry
|October 30, 2025
Summary
This study reports new mixed-valent dinickel complexes with a naphthyridine-based pincer ligand. These complexes exhibit a Ni-Ni bond and Class III mixed valence, with tunable redox properties.
Area of Science:
- Coordination Chemistry
- Organometallic Chemistry
- Materials Science
Background:
- Mixed-valent metal complexes are crucial for understanding electron transfer and developing novel functional materials.
- Dinickel complexes offer unique electronic structures and reactivity due to the presence of two metal centers.
- Pincer ligands provide robust coordination environments, influencing the stability and properties of metal complexes.
Purpose of the Study:
- To synthesize and characterize a novel family of mixed-valent dinickel complexes featuring a naphthyridine-based PNNP(iPr) pincer ligand.
- To investigate the electronic structure, bonding, and redox properties of these dinickel complexes.
- To explore the potential for interconversion between different oxidation states using chemical redox agents.
Main Methods:
- Synthesis of dinickel complexes via reaction of nickel(II) salts and Ni(COD)2 with the PNNP(iPr) ligand.
- Characterization using single-crystal X-ray diffraction, electron paramagnetic resonance (EPR), and magnetic susceptibility measurements.
- Electrochemical studies via cyclic voltammetry and UV-vis spectroscopy to probe redox properties and interconversion.
Main Results:
- Successful synthesis of three mixed-valent dinickel complexes: [Ni2(μ-Br)2PNNP(iPr)]2[NiBr4] (1), [Ni2(κ2-OAc)3PNNP(iPr)] (2), and [Ni2(κ2-OPiv)3PNNP(iPr)] (3).
- Confirmation of delocalized Ni2(3+) mixed valence and a Ni-Ni bond, classifying them as Class III mixed valence complexes.
- Observation of quasi-reversible Ni2(II,II)/Ni2(I,II) reduction events with E1/2 values between -0.83 V and -1.05 V vs. ferrocene/ferrocenium.
- Demonstration of interconversion between mixed-valent and Ni2(II,II) states via chemical oxidation or reduction.
Conclusions:
- The naphthyridine-based PNNP(iPr) ligand effectively stabilizes mixed-valent dinickel complexes with a Ni-Ni bond.
- These complexes exhibit robust redox activity and can be reversibly interconverted between different oxidation states.
- The findings contribute to the understanding of mixed-valence systems and offer potential for applications in catalysis or molecular electronics.
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